The present invention relates to both the mechanical and the electronic ammonia fertilizer application systems for agricultural use.
The typical electronically controlled ammonia application systems consist of a nurse tank trailed behind a tool bar which is attached to a tractor. A computer console is mounted accessible to the tractor operator.
The nurse tank is a pressure vessel which contains the ammonia in its liquid state. The liquid withdrawal valve is mounted at the top of the tank and has a dip tube which extends to the bottom of the tank. A suitable hose connects this valve to a filter connected to a main shutoff valve mounted on the tool bar. The ammonia then flows through a heat exchanger unit, then through a turbine or venturi meter, then to an electronically controlled throttling valve, then to one or more manifolds, and finally through suitable hoses to the applicator knives which inject the ammonia into the soil.
The typical mechanical systems are about the same as the electronic systems, however they utilize manually adjustable mechanical meters downstream of a heat exchanger unit.
As the liquid ammonia enters the dip tube located at the bottom of the tank, its thermodynamic conditions begin to change. The ammonia begins to expand. This results in the formation of ammonia vapor within the system which must be removed by a heat exchanger unit prior to metering in order to assure a proper quantity of ammonia to the applicator knives. The swath width of the tool bar and the desired amount of ammonia per acre are entered into the computer. The computer receives signals from either a turbine or venturi type meter and from the ground speed sensor. The computer processes the data and compensates for any variations by electronically controlling the throttling valve.
These systems work fairly well, but under certain conditions problems can arise. They lose all control of the ammonia as soon as it crosses the throttling valve. In cooler weather the pressure difference across the system is reduced and sagging hoses can cause the formation of plugs of liquid ammonia which result in uneven distribution to the applicator knives. Crops such as corn require more than twice the amount of ammonia per acre than the smaller grain crops. The greater expansion of the ammonia across the total system often forms more vapor than the typical heat exchanger unit can handle.
The most efficient source of nitrogen is anhydrous ammonia, which is stored within tanks as a liquefied gas. The vapor pressure contained within the upper portion of the tank moves the liquid ammonia to the withdrawal valve. The liquid ammonia stored within the tank contains potential energy in the form of heat which is used to move the ammonia after the vapor pressure in the tank has accelerated the liquid to the withdrawal valve. As the liquid crosses the high resistance at the withdrawal valve, there is a drop in pressure and temperature, which requires potential energy from the liquid. This energy produces ammonia vapor, requiring more volume for the mass which moves the product through the system. This results in a continual reduction in the mean product density which greatly hampers its management and metering. The ultimate result is an insufficient application of ammonia to the field and a reduction in crop yield,
The large food producers of the world with its increasing population can no longer afford the present inefficient anhydrous ammonia management systems. The proper management of the ammonia requires it to be in its liquid state as it crosses its metering devices, and means to provide compensation for the changes in liquid density for the electronic systems.
An ideal liquid ammonia temperature for proper metering would be 28 F. degrees with its liquid density at about 40 lbs/cubic foot. The only sensible method to achieve this is to maintain the pressure upon the liquid in the system by returning the vapor under pressure to the tank. The sun provides the energy to maintain the vapor pressure within the tank that moves the liquid to the withdrawal valve. When 100 lbs of liquid ammonia at 28 F. degrees leaves the tank, there is a resulting loss of 2.5 cubic feet of space within the tank which must be replaced by either the evaporation of 0.498 lbs of liquid ammonia or by the returning of the stripped vapor from downstream to the tank. This vapor has only kinetic energy, while the liquid in the tank has only potential energy until it is accelerated.
It would be a distinct advantage to have an ammonia control device which would provide the means necessary to reduce the volume of the ammonia within the system to a state of total liquid, which would provide for greater control, and application accuracy. The present invention provides such a unit.